6533b82ffe1ef96bd1296400

RESEARCH PRODUCT

Search for2βdecays of96Ru and104Ru by ultralow-background HPGeγspectrometry at LNGS: Final results

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An experiment to search for double-$\ensuremath{\beta}$ decay processes in ${}^{96}$Ru and ${}^{104}$Ru, which are accompanied by $\ensuremath{\gamma}$ rays, has been realized in the underground Gran Sasso National Laboratories of the I.N.F.N. (Italy). Ruthenium samples with masses of $\ensuremath{\approx}$0.5--0.7 kg were measured with the help of ultralow-background high-purity Ge $\ensuremath{\gamma}$-ray spectrometry. After 2162 h of data taking the samples were deeply purified to reduce the internal contamination of ${}^{40}$K. The last part of the data has been accumulated over 5479 h. New improved half-life limits on $2{\ensuremath{\beta}}^{+}/\ensuremath{\varepsilon}{\ensuremath{\beta}}^{+}/2\ensuremath{\varepsilon}$ processes in ${}^{96}$Ru have been established on the level of ${10}^{20}$ yr, in particular for decays to the ground state of ${}^{96}$Mo: ${T}_{1/2}^{2\ensuremath{\nu}2{\ensuremath{\beta}}^{+}}\ensuremath{\ge}1.4\ifmmode\times\else\texttimes\fi{}{10}^{20}$ yr, ${T}_{1/2}^{2\ensuremath{\nu}\ensuremath{\varepsilon}{\ensuremath{\beta}}^{+}}\ensuremath{\ge}8.0\ifmmode\times\else\texttimes\fi{}{10}^{19}$ yr, and ${T}_{1/2}^{0\ensuremath{\nu}2K}\ensuremath{\ge}1.0\ifmmode\times\else\texttimes\fi{}{10}^{21}$ yr (all limits are at 90$%$ C.L.). The resonant neutrinoless double-electron captures to the 2700.2 and 2712.7 keV excited states of ${}^{96}$Mo are restricted as ${T}_{1/2}^{0\ensuremath{\nu}KL}\ensuremath{\ge}2.0\ifmmode\times\else\texttimes\fi{}{10}^{20}$ yr and ${T}_{1/2}^{0\ensuremath{\nu}2L}\ensuremath{\ge}3.6\ifmmode\times\else\texttimes\fi{}{10}^{20}$ yr, respectively. Various two-neutrino and neutrinoless $2\ensuremath{\beta}$ half-lives of ${}^{96}$Ru have been estimated in the framework of the quasiparticle random-phase approximation approach. In addition, the ${T}_{1/2}$ limit for $0\ensuremath{\nu}2{\ensuremath{\beta}}^{\ensuremath{-}}$ transitions of ${}^{104}$Ru to the first excited state of ${}^{104}$Pd has been set as $\ensuremath{\ge}6.5\ifmmode\times\else\texttimes\fi{}{10}^{20}$ yr.